Angiogenesis is required for development of solid tumors. Mitochondrial function is linked to angiogenesis, because mitochondria are major sites of oxygen consumption and angiogenesis is an oxygen concentration-sensitive process (Andreyev, A. Y., Kushnareva, Y. E., and Starkov, A. A. (2005). Mitochondrial metabolism of reactive oxygen species. Biochemistry (Mosc.) 70, 200-214; and Maulik, N., and Das, D. K. (2002). Redox signaling in vascular angiogenesis. Free Radic. Biol. Med. 33, 1047-1060). Further, it is known that changes in the mitochondrial redox state stimulate production of reactive oxygen species (ROS) during hypoxia and mitochondrial ROS activate transcription of proangiogenic proteins (Chandel, N. S., Maltepe, E., Goldwasser, E., Mathieu, C. E., Simon, M. C., and Schumacker, P. T. (1998). Mitochondrial reactive oxygen species trigger hypoxia-induced transcription. Proc. Natl. Acad. Sci. USA 95, 11715-11720). According to articles published in scientific journals, production of ROS at the mitochondrial complex III is a necessary and sufficient condition for triggering of HIF-1α stabilization during hypoxia (Brunelle, J. K., Bell, E. L., Quesada, N. M., Vercauteren, K., Tiranti, V., Zeviani, M., Scarpulla, R. C., and Chandel, N. S. (2005). Oxygen sensing requires mitochondrial ROS but not oxidative phosphorylation. Cell Metab. 1, 409-414; Chandel, N. S., McClintock, D. S., Feliciano, C. E., Wood, T. M., Melendez, J. A., Rodriguez, A. M., and Schumacker, P. T. (2000). Reactive oxygen species generated at mitochondrial complex III stabilize hypoxia-inducible factor-1 during hypoxia. J. Biol. Chem. 275, 25130-25138; Guzy, R. D., Hoyos, B., Robin, E., Chen, H., Liu, L., Mansfield, K. D., Simon, M. C., Hammerling, U., and Schumacker, P. T. (2005). Mitochondrial Complex III is required for hypoxia-induced ROS production and cellular oxygen sensing. Cell Metab. 1, 401-408; and Mansfield, K. D., Guzy, R. D., Pan, Y., Young, R. M., Cash, T. P., Schumacker, P. T., and Simon, M. C. (2005). Mitochondrial dysfunction resulting from loss of cytochrome c impairs cellular oxygen sensing and hypoxic HIF-alpha activation. Cell Metab. 1, 393-399). Cells deficient in mitochondrial DNA and electron transport activity (ρo cells) exhibit no increase of ROS or no upregulation of HIF-1α target genes during hypoxia. Complex III inhibitors suppress mitochondrial ROS production during hypoxia and inhibit stabilization and transcriptional activity of HIF-1α. These findings suggest that ROS production at the mitochondrial complex III is a crucial event in signaling of cellular hypoxia. From the fact that structural components of the mitochondrial complex III take part in cellular oxygen sensing, it is believed that low-molecular weight compounds inhibiting such a cellular oxygen-sensing pathway will be useful means for inhibition of hypoxia-induced angiogenesis.
Meanwhile, biological screening tools are useful for identification of natural compounds capable of inducing alterations of certain phenotypic traits (Kwon, H. J. (2003). Chemical genomics-based target identification and validation of anti-angiogenic agents. Curr. Med. Chem. 10, 717-726; and Liu, J., Farmer, J. D. Jr., Lane, W. S., Friedman, J., Weissman, I., and Schreiber, S. L. (1991). Calcineurin is a common target of cyclophilin-cyclosporin A and FKBP-FK506 complexes. Cell 66, 807-815). In order to find compounds capable of inhibiting angiogenic responses in response to proangiogenic stimuli (such as hypoxia) in endothelial cells, the present inventors extensively conducted large-scale screening of microbial extracts. As a result, the present inventors succeeded in identification of bicyclo sesterterpene, e.g. terpestacin and found that terpestacin is a candidate material capable of inhibiting angiogenic responses at a concentration below a toxic threshold (Jung, H. J., Lee, H. B., Kim, C. J., Rho, J. R., Shin, J., and Kwon, H. J. (2003). Anti-angiogenic activity of terpestacin, a bicyclo sesterterpene from Embellisia chlatnydospora. J. Antibiotics 56, 492-496).
Terpestacin strongly inhibits angiogenic responses of human umbilical vein endothelial cells (HUVEC) in vitro, and strongly inhibits angiogenesis of embryonic chick chorioallantoic membrane (CAM) in vivo. Further, terpestacin is known to inhibit the formation of syncytium during HIV infections and can be chemically synthesized (Chan, J., and Jamison, T. F. (2004). Enantioselective synthesis of (−)-terpestacin and structural revision of siccanol using catalytic stereoselective fragment couplings and macrocyclizations. J. Am. Chem. Soc. 126, 10682-10691; Myers, A. G., Siu, M., and Ren, F. (2002). Enantioselective synthesis of (−)-terpestacin and (−)-fusaproliferin: clarification of optical rotational measurements and absolute configurational assignments establishes a homochiral structural series. J. Am. Chem. Soc. 124, 4230-4232; and Oka, M., Iimura, S., Tenmyo, O., Sawada, Y., Sugawara, M., Ohkusa, N., Yamamoto, H., Kawano, K., Hu, S. L., Fukagawa, Y., and Oki, T. (1993). Terpestacin, a new syncytium formation inhibitor from Arthrinium sp. J. Antibiotics 46, 367-373).
The mitochondrial complex III consists of eleven protein subunits. Essential components of the complex III, e.g. cytochrome b, cytochrome c1, Rieske iron-sulfur protein and ubiquinone are functionally well understood (Crofts, A. R., and Berry, E. A. (1998). Structure and function of the cytochrome bc1 complex of mitochondria and photosynthetic bacteria. Curr. Opin. Struct. Biol. 8, 501-509; and Smith, J. L., Zhang, H., Yan, J., Kurisu, G., and Cramer, W. A. (2004). Cytochrome be complexes: a common core of structure and function surrounded by diversity in the outlying provinces. Curr. Opin. Struct. Biol. 14, 432-439). In addition, specific inhibitors, for example, antimycin A, stigmatellin and myxothiazol have been widely used in functional studies of the complex III (Xia, D., Yu, C. A., Kim, H., Xia, J. Z., Kachurin, A. M., Zhang, L., Yu, L., and Deisenhofer, J. (1997). Crystal structure of the cytochrome bc1 complex from bovine heart mitochondria. Science 277, 60-66; Zhang, Z., Huang, L., Shulmeister, V. M., Chi, Y. I., Kim, K. K., Hung, L. W., Crofts, A. R., Berry, E. A., and Kim, S. H. (1998). Electron transfer by domain movement in cytochrome bc1. Nature 392, 677-684). Unfortunately, these compounds are not suitable as inhibitors of tumor angiogenesis, because they exhibit disadvantages such as inhibition of electron transport, abolition of oxidative phosphorylation, and induction of cellular apoptosis. For these reasons, there is a need for development of novel compounds deleting oxygen sensing functions of the complex III while not causing disruption of ATP production. Therefore, this is attracting a great deal of interest particularly from cancer biologists who have been focused on inhibition of adaptive responses (for example, expression of vascular endothelial growth factor) to hypoxia.
Throughout the specification, numerous scientific articles and patent publications are cited and citations thereof are identified. Disclosures of the cited articles and patent references are incorporated by reference herein in their entirety, such that a current status of a technical field to which the present invention pertains and the disclosure of the present invention will be more clearly described.